| Human beings appeared and developed rapidly during Quaternary, so it seemed particularly important to do some research on it. Explore environmental evolution in such a short period required a dating method which was more accurate and had higher resolution. Different dating methods had different strengths and limitations, however, the ESR(Electron spin resonance) dating method was widely used for covering almost the whole Quaternary. Caohai basin, a structural karst basin, was located in Yunnan-Guizhou Plateau. It had developed in arc anticline axis of Weining since late Pliocene, without supplemental water from distal river. Sediments that recorded evolution of basin were basic from the mountain around. Therefore, it was a remarkable place to study Quaternary evolution of Yunan-Guizhou Plateau.This study chose CXT section as research object, which was lacustrine strata of Weining Caohai area in Guizhou province. Using ESR dating methods to determine depositional age, with history of Tibetan Plateau uplift and contents and vertical distribution characteristics of environmental parameters such as chromaticity, particle size, magnetic parameters and geochemical elements, in order to preliminarily speculate and restore the paleo-environment characteristics and evolution of Caohai basin. This study concluded as follow:(1) The result of ESR dating to Caohai sediments were 1.16-1.87 Ma years ago, it was more accurate than the result of paleo-magnetic. Dating result was corresponding to the Tibetan movement C curtain in the early Pleistocene. The paleo-climate of Caihai basin could be warm and humid according to the effort of southwest monsoon.(2) Chromaticity result of Caohai sediments showed that brightness value was high, red and yellow value was low. We could speculate that Caihai basin was a deep-water environment with reduction and warm-wet climate at that time.(3) Particle size distribution of Caohai sediments was relatively concentrated. The major constituents of particle size were clay and powder sand. The grain sorting of profile was poor. So, paleo-environment should be river or lake in a period of high water level with humid climate.(4) Frequency magnetic susceptibility and remanence of Caohai sediments indicated that paleo-environment was warm and moist. However, the magnetic susceptibility indicated the dry and cold paleo-environment. Some research showed that magnetic susceptibility could not totally reflect the magnetic characteristic of samples in a real environment, or might miss some environmental information. So, magnetic susceptibility wasn’t treated as an ancient environmental proxies. Magnetic parameters that were consistent with chromaticity and granularity, indicated warm and moist paleo-environment.(5) We selected B, Sr, Mg/Al, Sr/Ba, Sr/Cu and B/Ga to represent the element geochemical characteristics of Caohai sediments for multi-index analysis of paleo-environment. Results all showed that sedimentary paleo-environment was humid with deep water.(6) The results between ESR dating and environmental proxies were the same, showed that the ESR dating method was relatively accurate and had scientific reference value. |
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